Comment # 9 on bug 982329 from Liuhua Wang

(In reply to Manfred Hollstein from comment #6)
> FWIW2: I just tried to reject /dev/loop devices from lvm's filter by adding
> 
>   "r|/dev/loop.*|", 
> 
> to devices/filter in /etc/lvm/lvm.conf, set max_loop to 64, rebuilt
> everything required, rebooted and failed again. Even if the /dev/loop
> devices are explicitly excluded in lvm.conf, they appear to be scanned when
> the system is booted, and 64 non-existing loop devices appear to be too many
> to allow the dm/udev logic in the latest lvm2 package to succeed.
> 
> I'm now back to max_loop set to 32 :(

In case of use_lvmetad = 0, the effective filter is "devices/filter"; while
in case of use_lvmetad = 1, the effective filter is "devices/global_filter".
Please see the comment about this:

    # Since "filter" is often overridden from command line, it is not suitable
    # for system-wide device filtering (udev rules, lvmetad). To hide devices
    # from LVM-specific udev processing and/or from lvmetad, you need to set
    # global_filter. The syntax is the same as for normal "filter"
    # above. Devices that fail the global_filter are not even opened by LVM.

    # global_filter = []

So in your case you need to add this to your lvm.conf.
    global_filter = ["r|/dev/loop.*|", "a/.*/"]